1. Field of the Invention
The present invention relates to air bearing spindles used for disk media test equipment such as disk certifiers.
2. Background Information
Hard disk drives contain magnetic recording heads that magnetize and sense the magnetic field of rotating disks. Each disk is constructed from a substrate that is coated with magnetic material. Manufacturing tolerances and process variations may vary the magnetic properties of the disks. It is desirable to test the disks to insure compliance with design specifications.
The disks are typically tested on an apparatus commonly referred to as a disk certifier in a process commonly referred to as "disk certification". Disk certifiers commonly use a spindle to rotate a disk adjacent to a magnetic recording head. The spindles used to spin the disk under test usually employ an air bearing due to the tight tolerances necessary for disk certification. The recording head writes and then reads data from the rotating disk. The data is then analyzed by test circuitry to determine whether the disk meets desired design specifications.
The disks are typically mounted onto the spindle by a robotic arm. There is a concern that the robotic arm may strike and damage the spindle. A damaged spindle may wobble and create a run-out in the disk. The disk run-out will reduce the accuracy of the test. It is therefore desirable to provide a spindle that is rugged enough to withstand the force of a robotic arm or other abuses to the spindle motor during the process of disk certification.
The air bearing of the spindle is typically created by providing pressurized air to a gap which separates a bearing(s) from a spindle housing. The pressurized air is typically providing by a pressurized air source at the site facility where the certifier is located. It has been found that some sites have lower air pressure than other sites. For example, air pressure provided by facilities within Japan is typically 60 psi. This is to be contrasted with sites within the United States where the air pressure can be 110 psi. The lower air pressure at the Japanese facilities will result in an air bearing which has a lower stiffness than air bearings created within the same spindle at a site within the United States. It would be desirable to provide a spindle with an air bearing that is stiffer than air bearings of the prior art. It would also be desirable to provide a pressurized air bearing spindle that also contains a self-acting air bearing characteristic to compensate for facility sites which have relatively low air pressure. It would also be desirable to provide an air bearing spindle that increases stiffness with an increase in speed to minimize instabilities or vibration in the spindle.